Vehicle heating and/or air conditioning method

ABSTRACT

The invention relates to a method for the heating and/or air conditioning of the passenger compartment of an automobile using a reversible cooling loop in which flows a coolant containing 2,3,3,3-tetrafluoropropene. The method is particularly useful when outdoor temperature is lower than −15° C. The method can be used for hybrid automobiles designed for operating alternatively with a thermal engine and an electric motor.

The present invention relates to a device for heating and/or air conditioning the passenger compartment of an automobile.

In automobiles, the thermal engine has a circuit in which flows a heat transfer fluid which is used for cooling the engine and also for heating the passenger compartment. For this purpose, the circuit comprises, notably, a pump and an air heater which recovers the heat stored by the heat transfer fluid in order to heat the passenger compartment.

Additionally, an air conditioning system for cooling the passenger compartment comprises an evaporator, a compressor, a condenser, an expansion valve and a fluid, commonly known as a coolant which can change its state (between liquid and gas). The compressor, driven directly by the vehicle engine by means of a belt and pulley, compresses the coolant and sends it back under high pressure and at high temperature toward the condenser. The condenser is provided with forced ventilation, causing the condensation of the gas which arrives in the gaseous state at high pressure and temperature. The condenser liquefies the gas as a result of the reduction of the temperature of the air flowing through it. The evaporator is a heat exchanger which draws heat from the air which is to be blown into the passenger compartment. The expansion valve can be used to regulate the inflow of the gas into the loop by a modification of the passage cross section depending on the temperature and pressure at the evaporator. Thus the hot air from outside the vehicle is cooled as it flows through the evaporator.

The coolant which is commonly used in automobile air conditioning is 1,1,1,2-tetrafluoroethane (HFC-134a). Document WO 2008/107623 describes an automobile energy management system comprising a reversible cooling loop through which a coolant flows, means for reversing the operating cycle of the cooling loop, which can move between a cooling mode position and a heat pump mode position, at least a first source for recovering energy from the coolant, and at least a second source for evaporating the coolant after the expansion of said fluid from the liquid to the two-phase state, the reversal means enabling coolant to flow from the first recovery source toward at least one evaporation source, when they are in a position identical to that corresponding to the heat pump mode.

However, when HFC-134a is used as the coolant in a system such as that described in WO 2008/107623, and when the outside temperature is approximately −15° C., a pressure drop starts to develop in the evaporator even before the compressor is started. This pressure drop, which leads to infiltration of air into the system, promotes corrosion phenomena and the degradation of the components such as the compressor, exchanger and expansion valve.

The object of the present invention is to prevent the air from penetrating into the evaporator of the cooling loop when the compressor is started, and/or to improve the efficiency of the cooling loop.

The present invention therefore proposes a heating and/or air conditioning method for a passenger compartment of an automobile, using a reversible cooling loop, in which a coolant flows, comprising a first heat exchanger, an expansion valve, a second heat exchanger, a compressor and means for reversing the direction of flow of the coolant, characterized in that the coolant comprises 2,3,3,3-tetrafluoropropene.

The means for reversing the direction of flow of the coolant in the cooling loop in order to reverse the operating cycle of the loop can be a four-way valve.

In addition to the 2,3,3,3-tetrafluoropropene, the coolant can comprise saturated or unsaturated hydrofluorocarbons.

Examples of saturated hydrofluorocarbons which may be mentioned are, notably, difluoromethane, difluoro-ethane, tetrafluoroethane and pentafluoroethane.

Examples of unsaturated hydrofluorocarbons which may be mentioned are, notably, 1,3,3,3-tetrafluoropropene, trifluoropropenes such as 3,3,3-trifluoropropene, and monochlorotrifluoropropenes such as 1-chloro,3,3,3-trifluoropropene and 2-chloro,3,3,3-trifluoropropene.

The following compositions may be suitable for use as coolants in the method according to the present invention:

-   -   80% to 98% by weight of 2,3,3,3-tetrafluoropropene and 2% to 20%         by weight of difluoromethane,     -   40% to 95% by weight of 2,3,3,3-tetrafluoropropene and 5% to 60%         by weight of 1,1,1,2-tetrafluoroethane,     -   90% to 98% by weight of 2,3,3,3-tetrafluoropropene and 2% to 10%         by weight of difluoroethane,     -   90% to 98% by weight of 2,3,3,3-tetrafluoropropene and 2% to 10%         by weight of pentafluoroethane.

The following compositions are especially suitable for use as coolants:

-   -   90% to 98% by weight of 2,3,3,3-tetrafluoropropene and 2% to 10%         by weight of difluoromethane,     -   90% to 95% by weight of 2,3,3,3-tetrafluoropropene and 5% to 10%         by weight of 1,1,1,2-tetrafluoroethane,     -   95% to 98% by weight of 2,3,3,3-tetrafluoropropene and 2% to 5%         by weight of difluoroethane,     -   95% to 98% by weight of 2,3,3,3-tetrafluoropropene and 2% to 5%         by weight of pentafluoroethane.

A composition which essentially contains 2,3,3,3-tetrafluoropropene is particularly preferred.

The coolant can also comprise stabilizers of the 2,3,3,3-tetrafluoropropene. Examples of stabilizer which may be mentioned are, notably, nitromethane, ascorbic acid, terephthalic acid azoles such as tolutriazole or benzotriazole, phenolic compounds such as tocopherol, hydroquinone, t-butyl hydroquinone, 2,6-di-tert-butyl-4-methylphenol, epoxides (alkyl which may be fluorinated or perfluorinated or alkenyl or aromatic) such as n-butyl glycidyl ethers, hexanediol diglycidyl ethers, allyl glycidyl ether, butylphenyl glycidyl ethers, phosphites, phosphates, phosphonates, thiols and lactones.

Depending on the operating mode of the loop, which may be the cooling or heat pump mode, the first heat exchanger can act as an evaporator or as an energy recovery unit. The same is true of the second heat exchanger. In cooling mode, the second exchanger can be used for cooling the air flow which is to be blown into the passenger compartment of the automobile. In heat pump mode, the second exchanger can be used to heat the air flow intended for the passenger compartment of the automobile. The first and second heat exchangers are of the air/coolant type.

In the method according to the present invention, the cooling loop can be thermally coupled through the heat exchangers to the entire cooling circuit. Thus the loop can comprise at least one heat exchanger through which the coolant and a heat transfer fluid flow simultaneously, the heat transfer fluid being, notably, the air or water of the thermal engine cooling circuit.

In a variant of the method, both the coolant and the exhaust gases from the thermal engine of the automobile flow through the first heat exchanger simultaneously; these fluids can communicate thermally by means of a heat transfer fluid circuit.

In the method according to the present invention, the cooling loop can include a branch having at least one heat exchanger communicating thermally with a flow of air which is to be admitted into the thermal engine of the automobile, or with exhaust gases emitted by the thermal engine of the automobile.

The method according to the present invention is particularly suitable when the outside temperature is below −15° C., or preferably below −20° C.

The method according to the present invention is equally suitable for hybrid automobiles designed to operate alternatively with a thermal engine and an electric motor. It can be used to provide the best management of the energy contributions according to the climatic conditions (hot or cold) for both the passenger compartment and the battery, and notably to supply heat or cold to the battery through a heat transfer fluid circuit.

The reversible cooling loop, in which the coolant containing 2,3,3,3-tetrafluoropropene flows, installed in automobiles is particularly suitable for the recovery of energy from the thermal engine and/or from the electrical battery, for use in heating the passenger compartment and for heating the thermal engine during a cold start phase. When this reversible cooling loop comprises a pump, it can operate in Rankine mode (that is to say, the compressor acts as a turbine) to exploit the thermal energy produced by the thermal engine and subsequently conveyed by the coolant, after heat transfer.

The invention also proposes a device comprising the cooling loop as described above.

In a first embodiment of the invention, illustrated schematically in FIG. 1, the cooling loop (16) comprises a first heat exchanger (13), an expansion valve (14), a second heat exchanger (15), a compressor (11) and a four-way valve (12). The first and second heat exchangers are of the air/coolant type. The coolant of the loop (16) and the air flow supplied by a fan pass through the first heat exchanger (13). Some or all of this air flow also passes through a heat exchanger of the engine cooling circuit (not shown in the drawing). In the same way, an air flow supplied by a fan passes through the second exchanger (15). Some or all of this air flow also passes through another heat exchanger of the engine cooling circuit (not shown in the drawing). The direction of flow of the air is a function of the operating mode of the loop (16) and of the requirements of the thermal engine. Thus, when the thermal engine is in stationary mode and the loop (16) is in heat pump mode, the air can be heated by the exchanger of the thermal engine cooling circuit, and can then be blown on to the exchanger (13) to accelerate the evaporation of the fluid of the loop (16) and thereby improve the performance of this loop. The exchangers of the cooling circuit can be activated by means of valves according to the requirements of the thermal engine (for heating the air entering the engine or for exploiting the energy produced by this engine).

In cooling mode, the coolant propelled by the compressor (11) flows through the valve (12) and then through the exchanger (13) which acts as a condenser (that is to say, it releases heat to the outside), and subsequently through the expansion valve (14) and then through the exchanger (15) which acts as an evaporator for cooling the air flow which is to be blown into the passenger compartment of the automobile.

In heat pump mode, the direction of flow of the coolant is reversed by means of the valve (12). The heat exchanger (15) acts as a condenser, while the exchanger (13) acts as an evaporator. The heat exchanger (15) can then be used to heat the air flow intended for the passenger compartment of the automobile.

In a second embodiment of the invention, shown schematically in FIG. 2, the cooling loop (26) comprises a first heat exchanger (23), an expansion valve (24), a second heat exchanger (25), a compressor (21), a four-way valve (22) and a branch (d3) connected at one end to the outlet of the exchanger (23) and at the other end to the outlet of the exchanger (25), with respect to the flow of the fluid in cooling mode. This branch comprises a heat exchanger (d1), through which an air flow or a flow of exhaust gas to be admitted into the thermal engine passes, and an expansion valve (d2). The first and second heat exchangers (23 and 25) are of the air/coolant type. The coolant of the loop (26) and the air flow supplied by a fan pass through the first heat exchanger (23). Some or all of this air flow also passes through a heat exchanger of the engine cooling circuit (not shown in the drawing). In the same way, an air flow supplied by a fan passes through the second exchanger (25). Some or all of this air flow also passes through another heat exchanger of the engine cooling circuit (not shown in the drawing). The direction of flow of the air is a function of the operating mode of the loop (26) and of the requirements of the thermal engine. By way of example, when the thermal engine is in stationary mode and the loop (26) is in heat pump mode, the air can be heated by the exchanger of the thermal engine cooling circuit, and can then be blown on to the exchanger (23) to accelerate the evaporation of the fluid of the loop (26) and thereby improve the performance of this loop.

The exchangers of the cooling circuit can be activated by means of valves according to the requirements of the thermal engine (for heating the air entering the engine or for exploiting the energy produced by this engine).

The heat exchanger (d1) can also be activated according to the energy requirements in either cooling or heat pump mode. Check valves can be fitted in the branch (d3) to activate or disable this branch.

A flow of air supplied by a fan passes through the exchanger (d1). The same air flow can pass through another heat exchanger of the engine cooling circuit and also through other exchangers placed in the exhaust gas circuit, on the air intake of the engine, or on the battery in a hybrid automobile.

In a third embodiment of the invention, illustrated schematically in FIG. 3, the cooling loop (36) comprises a first heat exchanger (33), an expansion valve (34), a second heat exchanger (35), a compressor (31) and a four-way valve (32). The first and second heat exchangers (33 and 35) are of the air/coolant type. The operation of the exchangers (33 and 35) is identical to that of the first embodiment shown in FIG. 1. Two fluid/liquid exchangers (38 and 37) are fitted both in the cooling loop circuit (36) and in the thermal engine cooling circuit or in a secondary glycol-water circuit. The fitting of the fluid/liquid exchangers without the use of an intermediate gaseous fluid (air) flowing through them contributes to an improvement of the heat exchange with respect to air/fluid exchangers. In a fourth embodiment of the invention, illustrated schematically in FIG. 4, the cooling loop (46) comprises a first heat exchanger set (43 and 48), an expansion valve (44), a second heat exchanger set (45 and 47), a compressor (41) and a four-way valve (42). A branch (d1) having one end connected to the outlet of the exchanger (43) and the other end connected to the outlet of the exchanger (47), with respect to the flow of the fluid in cooling mode. This branch comprises a heat exchanger (d1), through which an air flow or a flow of exhaust gas to be admitted into the thermal engine passes, and an expansion valve (d2). The operation of this branch is identical to that of the second embodiment shown in FIG. 2.

The heat exchangers (43 and 45) are of the air/coolant type and the exchangers (48 and 47) are of the liquid/coolant type. The operation of these exchangers is identical to that of the third embodiment shown in FIG. 3.

EXPERIMENTAL SECTION

Simulations of the performance of the coolant in the heat pump operating conditions in vehicles are given below, for a condenser temperature of 30° C. Condensation temperature: +30° C. (T cond)

Temperature at the compressor inlet: +5° C. (Te comp)

Evap P is the pressure at the evaporator.

Cond P is the pressure at the condenser.

T outlet comp is the temperature at the compressor outlet.

Rate: the compression rate is the ratio of the high pressure to the low pressure.

COP: this is the coefficient of performance and is defined, in the case of a heat pump, as the useful thermal power supplied by the system divided by the power received or consumed by the system.

CAP: this is the cubic capacity, which is the heating capacity per unit of volume (kJ/m³).

% CAP or COP is the ratio of the value of the CAP or COP of 2,3,3,3-tetrafluoropropene (HFO-1234yf) to that of HFC-134a.

Isentropic efficiency of the compressor: this is the ratio between the real energy transmitted to the fluid and the isentropic energy.

The isentropic efficiency of the compressor is expressed as a function of the compression rate. (FIG. 5)

η=a+bτ+cτ ² +d·τ ³ +e·τ ⁴

η=isentropic efficiency τ: compression rate a, b, c and e: constants

The values of the constants a, b, c, d and e are determined from a standard efficiency curve, found in “Handbook of air conditioning and refrigeration”, by Shan K. Wang.

For HFC-134a, the COP and the pressure at the evaporator decrease with the evaporation temperature.

Temp evap P cond P Rate T outlet CAP Isentrop. evap (° C.) (kPa) (kPa) (p/p) comp (kJ/m³) eff. COPc HFC-134a −35.00 66.70 768.33 11.52 82.61 679.70 0.62 2.32 −30.00 84.92 768.33 9.05 75.31 841.71 0.68 2.82 −25.00 106.89 768.33 7.19 68.35 1032.37 0.75 3.39 −20.00 133.14 768.33 5.77 61.72 1255.21 0.79 4.01

For HFO-1234yf in the same conditions, we find:

Temp evap P cond P Rate T outlet CAP Isentrop. evap (° C.) (kPa) (kPa) (p/p) comp (kJ/m³) eff. COPc % cap % COP HFO-1234yf −35.00 77.05 772.09 10.02 70.15 707.00 0.66 2.43 104 104 −30.00 97.01 772.09 7.96 64.10 865.60 0.72 2.91 103 103 −25.00 120.73 772.09 6.40 58.36 1049.51 0.77 3.45 102 102 −20.00 148.64 772.09 5.19 52.88 1261.40 0.81 4.01 100 100

The evaporator pressure with HFO-1234yf is higher than with HFC-134a, thus helping to limit the infiltration of air into the system when the system operates at a very low temperature.

For a given compressor operating at very low temperature, the performance of HFO-1234yf is better than that of HFC 134a. In heating mode and when the condensation temperature is 30° C., the use of HFO-1234yf yields better efficiency at the compressor, better COP and better capacity. 

1. A heating and/or air conditioning system for a passenger compartment of an automobile having a thermal engine having a cooling circuit through which an engine coolant flows and/or an electrical battery comprising a reversible cooling loop in which a coolant flows, said reversible cooling loop comprising a first heat exchanger, an expansion valve, a second heat exchanger, a compressor and means for reversing the direction of flow of the coolant, characterized in that the coolant comprises 2,3,3,3-tetrafluoropropene.
 2. (canceled)
 3. The system as claimed in claim 1, characterized in that the first heat exchanger and the second exchangers are of the air/coolant type.
 4. The system as claimed in claim 1, further characterized in that the reversible cooling loop is thermally coupled to the cooling circuit of the thermal engine of said automobile.
 5. The system as claimed in claim 1, characterized in that both the engine coolant and exhaust gases from the thermal engine of the automobile flow through the first heat exchanger simultaneously.
 6. The system as claimed in claim 1, characterized in that the reversible cooling loop further comprises a branch having at least one heat exchanger communicating thermally with a flow of air which is to be admitted into the thermal engine of the automobile, or with exhaust gases emitted by the thermal engine of the automobile.
 7. The system as claimed in claim 1, characterized in that the cooling loop recovers energy from the thermal engine and/or from the electrical battery.
 8. (canceled)
 9. A heating and/or air conditioning method for a passenger compartment of an automobile having a thermal engine having a thermal engine having a cooling circuit through which an engine coolant flows and/or an electrical battery, comprising flowing a coolant through a reversible cooling loop comprising a first heat exchanger, an expansion valve, a second heat exchanger, a compressor and means for reversing the direction of flow of the coolant, characterized in that the coolant comprises 2,3,3,3-tetrafluoropropene.
 10. The method as claimed in claim 9, characterized in that the first and second exchangers are of the air/coolant type.
 11. The method as claimed in claim 9, characterized in that the reversible cooling loop is thermally coupled to the cooling circuit of the thermal engine.
 12. The method as claimed in claim 9, characterized in that the engine coolant and exhaust gases from the thermal engine of the automobile flow through the first heat exchanger simultaneously.
 13. The method as claimed in 9, characterized in that the cooling loop further comprises a branch having at least one heat exchanger communicating thermally with a flow of air which is to be admitted into the thermal engine of the automobile or with exhaust gases emitted by the thermal engine of the automobile.
 14. The method as claimed claim 9, characterized in that the cooling loop recovers energy from the thermal engine and/or from the electrical battery. 